US6366588B1 - Method and apparatus for achieving data rate variability in orthogonal spread spectrum communication systems - Google Patents

Method and apparatus for achieving data rate variability in orthogonal spread spectrum communication systems Download PDF

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US6366588B1
US6366588B1 US09/032,166 US3216698A US6366588B1 US 6366588 B1 US6366588 B1 US 6366588B1 US 3216698 A US3216698 A US 3216698A US 6366588 B1 US6366588 B1 US 6366588B1
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rate
signal
rates
orthogonal function
data
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Michael James Gans
Laurence Eugene Mailaender
Yu Shuan Yeh
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Nokia of America Corp
WSOU Investments LLC
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Lucent Technologies Inc
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Assigned to LUCENT TECHNOLOGIES INC. reassignment LUCENT TECHNOLOGIES INC. ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: GANS, MICHAEL JAMES, MAILAENDER, LAURENCE EUGENE, YEH, YU SHUAN
Priority to US09/032,166 priority Critical patent/US6366588B1/en
Priority to CA002260522A priority patent/CA2260522C/en
Priority to DE69936112T priority patent/DE69936112T2/de
Priority to EP99301134A priority patent/EP0939508B1/en
Priority to AU18365/99A priority patent/AU1836599A/en
Priority to BR9917172-4A priority patent/BR9917172A/pt
Priority to CN99102437A priority patent/CN1123993C/zh
Priority to KR1019990006460A priority patent/KR100805643B1/ko
Priority to JP05312099A priority patent/JP3884184B2/ja
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Assigned to WSOU INVESTMENTS, LLC reassignment WSOU INVESTMENTS, LLC RELEASE BY SECURED PARTY (SEE DOCUMENT FOR DETAILS). Assignors: OCO OPPORTUNITIES MASTER FUND, L.P. (F/K/A OMEGA CREDIT OPPORTUNITIES MASTER FUND LP
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
    • H04B1/69—Spread spectrum techniques
    • H04B1/707—Spread spectrum techniques using direct sequence modulation
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04J—MULTIPLEX COMMUNICATION
    • H04J13/00—Code division multiplex systems
    • H04J13/0007—Code type
    • H04J13/004—Orthogonal
    • H04J13/0048—Walsh
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/24—Radio transmission systems, i.e. using radiation field for communication between two or more posts
    • H04B7/26—Radio transmission systems, i.e. using radiation field for communication between two or more posts at least one of which is mobile
    • H04B7/2628—Radio transmission systems, i.e. using radiation field for communication between two or more posts at least one of which is mobile using code-division multiple access [CDMA] or spread spectrum multiple access [SSMA]
    • H04B7/264—Radio transmission systems, i.e. using radiation field for communication between two or more posts at least one of which is mobile using code-division multiple access [CDMA] or spread spectrum multiple access [SSMA] for data rate control
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04J—MULTIPLEX COMMUNICATION
    • H04J13/00—Code division multiplex systems
    • H04J13/16—Code allocation
    • H04J13/18—Allocation of orthogonal codes

Definitions

  • the present invention relates to cellular and other communication systems, and more particularly, to methods and apparatus for achieving additional data rates in communication systems utilizing code division multiple access (CDMA).
  • CDMA code division multiple access
  • CDMA Code division multiple access
  • CDMA Code division multiple access
  • CDMA code division multiple access
  • TIA Telecommunication Industry Association
  • a communication system substantially eliminates co-channel interference and improves the bit energy-to-noise density ratio, E b /N o , on the forward link from a base station or cell site to a mobile receiver unit by modulating the information signals with Walsh orthogonal function sequences.
  • E b /N o bit energy-to-noise density ratio
  • these CDMA systems require that the forward link information signals be transmitted in a synchronized manner.
  • TIA/EIA/IS-95 (1993) A more detailed discussion of the IS-95 standard is provided in “Mobile Station-Base Station Compatibility Standard for Dual-Mode Wideband Spread Spectrum Cellular System,” Telecommunication Industry Association Doc. No. TIA/EIA/IS-95 (1993)[, incorporated by reference herein].
  • the document TIA/EIA/IS-95 (1993) may be obtained, for example, using the following Internet reference: http://www.tiaonline.org/standards/search_n_order.
  • IS-95B Current implementations of the IS-95 standard, however, allow only a limited number of data rates. Specifically, the Telecommunication Industry Association has recently adopted a new standard, IS-95B, for increasing the data rates that may be achieved with CDMA networks. The IS-95B standard, however, only permits data rates that are integer or power-of-two multiples of the basic CDMA rate. While such techniques satisfy the data rate needs of many applications, the utility of CDMA networks could be significantly extended if further data rate variability could be achieved.
  • a CDMA communication system offering a near continuum of data rates up to a maximum rate.
  • the disclosed CDMA communication system increases the data rate variability, without disturbing the orthogonality between users.
  • An increased number of data rates is obtained by time multiplexing the data rates achievable with conventional CDMA systems to provide additional data rates for various multimedia applications.
  • a user is assigned a specific orthogonal code sequence, such as a Walsh sequence, which permits a nominal data rate, R, and higher data rates, nR, the user can obtain additional desired data rates by time multiplexing the specific orthogonal code set.
  • desired bit rates are provided for applications requiring bit rates that are not an integer multiple of the rates provided by conventional “fat pipe” techniques.
  • any rate can be achieved, up to a rate of 4R.
  • Rates R, 2R, 4R and 16R can be achieved by assigning other appropriate code sets to the information source, in a conventional manner.
  • any desired rate up to 4R is achieved by time multiplexing the codes w k , w k 2 and w k 4 .
  • the transmitter of the present invention achieves a rate conversion to match the appropriate codeword to the appropriate data rate, by employing buffering and reclocking of the data, with time multiplexing of the orthogonal Walsh codes corresponding to the available lower and upper rates.
  • the rate conversion must be synchronized with the selection of the orthogonal Walsh code (corresponding to the lower and upper rates). For example, an application requiring a data rate between 2R and 4R, such as 2.3R, would require multiplexing of the 2R and 4R Walsh codes (w k 2 and w k 4 ) to achieve the desired 2.3R rate.
  • the sequence w 1 2 is utilized to achieve a rate of 2R and the sequence w 1 4 is utilized to achieve a rate of 4R, with an appropriate balance to achieve an overall 2.3R rate, and the codes w 5 , w 9 , w 13 are excluded from use.
  • FIG. 1 is a block diagram of a conventional CDMA transmitter that provides user streams (or sub-channels) at a single data rate;
  • FIG. 2 is a table of an illustrative set of orthogonal spread spectrum codes, w 0 through w 15 ;
  • FIG. 3 is a block diagram of a conventional CDMA transmitter that provides at least one information signal at an integer multiple of the data rate of FIG. 1;
  • FIG. 4 is a block diagram of a conventional CDMA transmitter that provides at least one information signal at two times the data rate of FIG. 1;
  • FIG. 5 is a block diagram of a conventional CDMA transmitter that transmits at least one information signal at four times the data rate of FIG. 1;
  • FIG. 6 is a block diagram of one sub-channel of a CDMA transmitter offering data rate variability in accordance with one embodiment of the present invention
  • FIG. 7 is a block diagram of one embodiment of the rate converter of FIG. 6.
  • FIG. 8 is a block diagram of a CDMA receiver offering data rate variability in accordance with one embodiment of the present invention.
  • the present invention relates to a method and apparatus for modulating a communication signal in a code division multiple access (CDMA) environment using orthogonal spread spectrum codes.
  • CDMA code division multiple access
  • conventional CDMA spread spectrum modulation techniques with orthogonal codes only permit data rates that are integer or power-of-two multiples of the chip rate.
  • the present invention improves on conventional CDMA spread spectrum modulation techniques by time multiplexing the data rates achievable with conventional CDMA systems to provide additional data rates for various multimedia applications.
  • a continuum of data rates are provided.
  • the predefined codeword may be utilized to represent a value of binary “0” and the inverse of the predefined codeword may be utilized to represent a value of binary “1.”
  • a number of orthogonal spread spectrum codes consisting of a number of consecutive positive and negative signal elements, such as Walsh codes, have been discovered which have unique properties that optimize the detection of the transmitted information.
  • Walsh codes For example, sixty four different Walsh codewords, w 0 through w 63 , each consisting of sixty four chips, permit 64 different information signals to be transmitted on the same carrier frequency. Since a number of channels are reserved for administration, such as the pilot, synch and paging channels, less than the available sixty four channels typically transmit user information.
  • sixteen different Walsh codewords, w 0 through w 15 each consisting of sixteen chips, permit up to sixteen different information signals, d 0 through d 15 , to be transmitted on the same carrier frequency.
  • a transmitter 100 encodes each of sixteen data streams, d 0 through d 15 , to be transmitted using one of sixteen different Walsh codewords, w 0 through w 15 .
  • the illustrative Walsh codewords, w 0 through w 15 are shown in FIG. 2 .
  • the encoded signals will then be combined and modulated in a conventional manner, prior to transmission over a transmission medium 130 .
  • the transmission medium 130 may be embodied as a conventional or wireless communications network.
  • the modulator may employ a modulation technique, for example, which multiplies the codeword by a sinusoidal carrier wave in order to shift the signal frequency upward to the carrier frequency (not shown). In this manner, the original signal spectrum may be translated into a particular frequency band allocated by the Federal Communications Commission (FCC) or another regulatory body.
  • FCC Federal Communications Commission
  • the frequency of the received signal is typically first shifted down (not shown) to the base band by a demodulator, thus returning the signal to its original form prior to modulation. Thereafter, the received signal is passed through a series of filters, such as filters 161 - 176 , that are each matched to the characteristics of the appropriate codeword, w 0 through w 15 .
  • filters 161 - 176 that are each matched to the characteristics of the appropriate codeword, w 0 through w 15 .
  • the receiver 150 may be associated with all sixteen end users 181 through 196 , as shown in FIG. 1 . More typically, however, each end user, such as end user 181 , will have its own receiver 150 .
  • each of the information sources 101 - 116 transmits at a uniform rate, R, and the symbol duration is equal to the Walsh code duration.
  • Additional data rate variability can be achieved within the implementation shown in FIG. 1, by assigning multiple orthogonal spread spectrum codes, such as Walsh codes, to the same high rate information source, such as the source 101 .
  • multiple orthogonal spread spectrum codes such as Walsh codes
  • 3R transmission rate
  • three Walsh codewords sub-channels
  • the set of achievable data rates are integer multiples of the symbol rate, R.
  • multicode source 101 will require additional buffering, typically in the form of a serial-to-parallel converter 310 .
  • the transmitter 100 ′ shown in FIG. 3 can combine any of the sixteen sub-channels associated with the codewords, w 0 through w 15 , to increase the data rate for a single information source 101 to a maximum of 16R.
  • a second well-known method for increasing the transmission rate in a code division multiple access (CDMA) network commonly referred to as the “fat pipe” method, “punctures” the set of illustrative Walsh codes shown in FIG. 2 .
  • the “fat pipe” method achieves data rates that are power-of-two multiples of the chip rate, without requiring buffering of the multiple rate user.
  • the achievable data rates are R, 2R, 4R, 8R and 16R (for the illustrative 16 dimensional Walsh codes shown in FIG. 2 ).
  • Specific code pairs such as the code pairs (w 0 , w 8 ) or (w 1 , w 9 ), are assigned to the double rate users, transmitting at rate 2R.
  • Each double rate user will encode data with only the first half of one of the assigned orthogonal spread spectrum codes.
  • the symbol, w k 2 denotes the first half of the spread spectrum code w k shown in FIG. 2 .
  • w 1 2 is utilized to encode data at a rate of 2R, and w 9 is excluded from use by all information sources.
  • w k+8 2 w k 2
  • the second half of the spread spectrum code w k+8 is the opposite polarity of the spread spectrum code w k .
  • specific code quadruples such as the code quadruples (w 0 , w 4 , w 8 , w 12 ) or (W 1 , w 5 , w 9 , w 13 ), are assigned to each quadruple rate user, transmitting at a rate 4R.
  • w 0 is utilized to encode data and w 4 , w 8 , and w 12 are excluded from use by all information sources.
  • w 1 is utilized to encode data and w 5 , w 9 and w 13 are excluded from use by all information sources.
  • the symbol, w k 4 denotes the first quarter of the spread spectrum code w k shown in FIG. 2 .
  • additional data rates are achieved while maintaining the orthogonal signal structure discussed above for conventional code division multiple access (CDMA) transmitters.
  • CDMA code division multiple access
  • a user if a user is assigned a specific code set in the manner described above, which permits a maximum data rate nR, the user can obtain additional desired data rates up to the maximum rate nR, by time multiplexing the specific code set.
  • conventional techniques would require “dummy” data, such as all zeros, to be added to the transmitted stream to bring the presented rate up to the next greatest available “fat pipe” rate, such as 4R.
  • the present invention provides desired bit rates for applications that have a bit rate that is not an integer multiple of the rates provided by the “fat pipe” technique discussed above.
  • any rate can be achieved, up to a rate of 4R. While the user can achieve a fundamental rate of R in the manner described above in conjunction with FIG. 1 by employing the spread spectrum code w 0 , a “fat pipe” rate of 2R in the manner described above in conjunction with FIG. 4 by employing the spread spectrum code w 0 2 , or a “fat pipe” rate of 4R in the manner described above in conjunction with FIG.
  • the user can achieve desired additional lower rates by time multiplexing the codes w 0 , w 0 2 and w 0 4 , to achieve rates between R and 4R.
  • the user can achieve any data rate that is a rational scale factor combination of the rates R and 4R.
  • the transmitter 600 of the present invention achieves a rate conversion by employing buffering and reclocking of the data, with time multiplexing of the orthogonal Walsh codes corresponding to the available lower and upper rates.
  • the rate conversion must be synchronized with the selection of the orthogonal Walsh code (corresponding to the lower and upper rates).
  • the illustrative 2.3R application would require multiplexing of the 2R and 4R Walsh codes to achieve the desired 2.3R rate.
  • the sequence w 1 4 is utilized to achieve a rate of 4R, and the codes w 5 , w 9 , w 13 are excluded from use.
  • the sync channel (or another administration channel) is preferably utilized to coordinate the wireless service.
  • the originating entity will send a message either requesting or confirming the rate, as well as the particular codes desired. For example, if the mobile terminal requests a channel having a 2.3R rate, the base station will grant or deny the request, and supply the assigned sequences, if available. In one preferred embodiment, the base station will supply the mobile terminal with the assigned sequences, as well as the amount of data that should be transmitted at each of the lower and upper rates.
  • the sync channel protocol may consist of a message containing a user identifier (indicating, for example, the mobile terminal), a sequence number (indicating the particular Walsh code, w 0 though w 15 , to utilize), the number of repetitions, N L and N U , and the rate exponents, R L and R U , for the lower and upper rates, respectively (such as 2R, 4R, or 8R).
  • a user identifier indicating, for example, the mobile terminal
  • a sequence number indicating the particular Walsh code, w 0 though w 15 , to utilize
  • the number of repetitions N L and N U
  • R L and R U the rate exponents
  • N L and N U are the number of symbols to transmit at each of the lower and upper rates, respectively.
  • R final is the desired rate to be achieved and R is the fundamental rate.
  • One method for determining this solution recognizes that 2.3 can be written as a ratio of the integers 23 and 10. Writing R final as this ratio, and using the above equation, leads to a system of linear equations:
  • the transmitter 600 of the present invention includes a rate converter 620 and a clock 630 to buffer and reclock the data, respectively, received from a high rate source 610 .
  • the rate converter 620 must be synchronized with the selection of the orthogonal Walsh code (corresponding to the lower and upper rates), w k L and w k U , by a switch 640 .
  • the output of the rate converter 620 exhibits two different bit durations, and the Walsh codes, w k L and w k U , are used accordingly to multiply the data by a multiplier 650 .
  • the information source has been matched to the existing fat pipe rates.
  • FIG. 7 illustrates one implementation of the rate converter 620 .
  • the rate converter 620 includes two buffers 710 and 720 .
  • the first buffer 710 fills with data at a constant rate
  • the second buffer 720 is read by an asymmetric multiplexer 730 for every (N L +N U ) bits.
  • N L 17 bits
  • N U the last 6 bits
  • R U the clock at the input of the buffer 710 is symmetric (evenly spaced)
  • the clock at the output of the asymmetric buffer 720 is asymmetric.
  • the clock 630 controls the buffer 720 , the asymmetric multiplexer 730 and the selection of the Walsh code by the switch 640 for the multiplier 650 .
  • FIG. 8 illustrates one implementation of a receiver 800 in accordance with the present invention.
  • the receiver 800 includes a multiplier 810 , which selectively multiplies the received data by the appropriate Walsh code, as selected by a switch 820 , an integrate, dump, detect block 830 for determining the received bit polarities, a rate converter 840 and a clock 850 .
  • the rate converter 840 operates in a similar manner to the rate converter 620 , discussed above in conjunction with FIGS. 6 and 7.
  • the selection of the low rate or upper rate Walsh waveform at the multiplier 810 is tied to the integrator 830 and the input clock of the rate converter 840 .
  • the input clock of the rate converter 840 is asymmetric while the output clock is symmetric.

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  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Mobile Radio Communication Systems (AREA)
  • Synchronisation In Digital Transmission Systems (AREA)
US09/032,166 1998-02-27 1998-02-27 Method and apparatus for achieving data rate variability in orthogonal spread spectrum communication systems Expired - Lifetime US6366588B1 (en)

Priority Applications (9)

Application Number Priority Date Filing Date Title
US09/032,166 US6366588B1 (en) 1998-02-27 1998-02-27 Method and apparatus for achieving data rate variability in orthogonal spread spectrum communication systems
CA002260522A CA2260522C (en) 1998-02-27 1999-01-28 Method and apparatus for achieving data rate variability in orthogonal spread spectrum communication systems
DE69936112T DE69936112T2 (de) 1998-02-27 1999-02-16 Verfahren und Vorrichtung zur Erzielung von Datenraten-Varietät in orthogonalen Spreizband-Nachrichtenübertragungssystemen
EP99301134A EP0939508B1 (en) 1998-02-27 1999-02-16 Method and apparatus for achieving data rate variability in orthogonal spread spectrum communications systems
AU18365/99A AU1836599A (en) 1998-02-27 1999-02-22 Method and apparatus for achieving data rate variability in orthogonal spread spectrum communication system
BR9917172-4A BR9917172A (pt) 1998-02-27 1999-02-26 Método e aparelho para obter variabilidade detaxa de dados em sistemas de comunicação deespectro difuso ortogonal
CN99102437A CN1123993C (zh) 1998-02-27 1999-02-26 正交扩展频谱通信系统中获取速率可变性的方法和设备
KR1019990006460A KR100805643B1 (ko) 1998-02-27 1999-02-26 직교 확산 스펙트럼 통신 시스템에서 데이터 레이트 가변성을 획득하기 위한 방법 및 장치
JP05312099A JP3884184B2 (ja) 1998-02-27 1999-03-01 通信システムにおける拡散スペクトラム信号の送信方法

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US6625136B1 (en) * 1998-07-20 2003-09-23 Telefonaktiebolaget Lm Ericsson (Publ) Spreader for multiple data rates
US6711121B1 (en) * 1998-10-09 2004-03-23 At&T Corp. Orthogonal code division multiplexing for twisted pair channels
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JP3884184B2 (ja) 2007-02-21
CN1123993C (zh) 2003-10-08
KR100805643B1 (ko) 2008-02-26
CA2260522A1 (en) 1999-08-27
EP0939508A3 (en) 2003-03-26
BR9917172A (pt) 2001-12-04
EP0939508B1 (en) 2007-05-23
JPH11298444A (ja) 1999-10-29
KR19990072969A (ko) 1999-09-27
DE69936112T2 (de) 2008-01-24
DE69936112D1 (de) 2007-07-05
EP0939508A2 (en) 1999-09-01
CN1233890A (zh) 1999-11-03
CA2260522C (en) 2006-09-05
AU1836599A (en) 1999-09-09

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